Generally, image sensors are semiconductor devices used to convert an optical image into an electric signal. The image sensors are typically classified into a charge coupled device (CCD) image sensor, which includes metal-oxide-semiconductor (MOS) capacitors closely adjacent to each other to store charge carriers therein and transfer the charge carriers; and a complementary MOS (CMOS) image sensor, which employs a switching mode to sequentially detect an output of each unit pixel by MOS transistors, in which the MOS transistors are formed on a semiconductor substrate corresponding to the unit pixels through a CMOS technology using peripheral devices, such as a controller and a signal processor.
The CMOS image sensor often includes a color filter formed over a pixel array to selectively supply light having a specific wavelength to a photodiode, thereby reproducing an image. The photodiode may be formed by performing an ion implantation process in a semiconductor substrate.
The CMOS image sensor according to the related art includes a transistor and a photodiode formed on one surface of a semiconductor substrate, and includes a metal interconnection formed over the photodiode and the transistor. However, the area of a light receiving part is restricted due to the routing of the metal interconnection. Light incident onto the light receiving part must pass through a multi-layer interlayer dielectric layer for the metal interconnection such that the light can be supplied to the photodiode. Accordingly, light loss occurs, so that the image sensitivity of the image sensor according to the related art may be degraded.
Further, since the number of metal interconnection layers is restricted in order to shorten an optical path from a micro-lens to a photodiode, design of the image sensor is restricted.